The present invention relates to improvements in centrifugal pumps of the type having double volute casings. More particularly, the invention relates to improvements in a centrifugal pump wherein the casing has two similar or identical volutes extending along arcs of maximally 180 degrees and facing each other across the axial passage of the casing. Such passage receives the pump shaft and the impeller which receives motion from the pump shaft, or a guide wheel which is installed downstream of the impeller.
The aforementioned commonly owned copending application for "Centrifugal pump with double volute casing" discloses that the dimensions of the casing can be reduced by selecting the outer diameter of the casing in such a way that it equals or approximates the outer diameter of the end of the first volute, namely, that portion of the first volute which is adjacent to the start of the second volute. The aforesaid copending application further discloses the possibility of providing a common outlet nozzle for the two volutes whereby the end of the second volute communicates directly with the outlet nozzle and the latter communicates with the end of the first volute by one or more channels which are provided in the casing and extend along the second volute.
The just described double volute casing exhibits the advantage that its weight, bulk and cost are a relatively small fraction of the weight, bulk and cost of heretofore known double volute casings, for example, casings of the type disclosed in German Offenlegungsschrift No. 26 40 866. However, and since the casings are normally made by resorting to a casting technique, the making of a double volute casing with one or more channels which flank the second volute and serve to connect the end of the first volute with an outlet nozzle for both volutes can present serious problems.